Teenage girls must be given lessons in how to say no to sex, a Conservative MP has told parliament – and MPs have backed her call.

Speaking in the Commons on Wednesday, Nadine Dorries, the MP for Mid Bedfordshire, proposed a bill that would result in classes in abstinence, but only for girls aged 13 to 16.

She said society was "saturated in sex" and teenagers should be taught that it was as "cool" to say no to sex as to know how to put a condom on their boyfriend.

MPs voted 67 to 61, majority six, in favour of allowing Dorries to bring forward her bill. It will receive its second reading in January, though it is unlikely to become law without government support.

The latest data from the Office for National Statistics show teenage pregnancies are at their lowest rate since the early 1980s. The under-18 conception rate for 2009 was 38.3 conceptions per 1,000 women aged 15 to 17. This represents a fall of 5.9% compared with 40.7 conceptions per 1,000 women aged 15 to 17 in 2008.

However, Dorries told MPs the sale of porn magazines in newsagents, and high street shops selling padded bikinis for seven-year-old girls showed "how far the sexualisation of young girls has gone in our society".

"The answer to ending our constant struggle with the incredibly high rate of teenage sexual activity and underage pregnancies lies in teaching our girls and boys about the option of abstinence, the ability to 'just say no', as part of their compulsory sex education," she said.

"Peer pressure is a key contributor to early sexual activity in our country. Society is focused on sex. Teaching a child at the age of seven to apply a condom on a banana is almost saying: 'Now go and try this for yourself'. By the age of 18, some girls have been taught three times how to put a condom on a boy.

"Girls are taught to have safe sex, but not how to say no to a boyfriend who insists on sexual relations." She said she had sat in on sex education classes in 17 schools and had spoken to teenage girls, many of whom "do not even think they have the option of saying no to boys", she said.

But Chris Bryant, a Labour MP who has led a campaign for primary school pupils to have compulsory sex education lessons, said Dorries' 10-minute rule bill was "the daftest piece of legislation" he had seen.

He said: "I am a gay man, so I'm not exactly an expert on heterosexual sex, nor on sex with girls. But ... this is not the way to solve any of those problems – for a start, it's just about girls. You've got to talk to the boys and the girls." He said there was no evidence that teaching abstinence would lead to fewer pregnancies or sexually transmitted diseases.

"The single most important thing we can do for any young person is give them the self-confidence to be able to make good decisions for themselves," he said.

He added that he had never understood why teaching pupils how to put a condom on a banana or a cucumber was "of any use to anybody".

The Family Planning Association charity said the bill reinforced sexual stereotypes.

A spokeswoman said young men also felt pressurised into having sex. "This bill is not helping them and does nothing to empower young women to take personal responsibility."

Dorries has courted controversy as one of England's most outspoken politicians.

The former nurse has criticised David Cameron's proposal to create all-women shortlists for prospective MPs.

Dorries has also campaigned to reduce the time during a pregnancy when an abortion can take place from 24 to 21 weeks.

In 2009, she was involved in a motion, discussed at the Trades Union Congress, to reduce the number of women wearing high heels at work. High heels give women lower limb pains, which mean they take time off work, the motion said.

• This article was amended on 4 May 2011. It said that Nadine Dorries had been accused of claiming expenses for furniture and gardening. This has been corrected